Carrington J L, Fallon J F
J Embryol Exp Morphol. 1984 Dec;84:19-34.
Reports on the stages when chick flank ectoderm can respond to ridge induction are contradictory. Different results have been obtained using presumptive wing or leg bud mesoderm as the inducing tissue with flank ectoderm as the responding tissue. In addition, although incomplete outgrowths have been obtained from recombinants with stage-19 flank ectoderm in a small percentage of cases, no complete outgrowths have been obtained from recombinants with ectoderm older than stage 18. We reinvestigated when chick flank ectoderm can respond to ridge induction and promote outgrowth of complete limbs. To do this, we combined flank ectoderm with in situ chick presumptive wing bud mesoderm using a pre-limb bud recombinant technique. When presumptive wing bud ectoderm was removed from the host and not replaced, wing development was suppressed. When host ectoderm was replaced with stage-15 through -18 chick flank ectoderm, limbs grew out in all cases; 86.4% of these recombinant limbs were distally complete. Stage-19 flank ectoderm formed a ridge and promoted limb outgrowth in 80.9% of recombinants; 52.9% of these were distally complete limbs. Recombinants made by grafting early stage-20 (40-somite donor) flank ectoderm to stage-15 hosts resulted in outgrowths in 60% of the cases and 33.3% of these were distally complete. Graft ectoderm from older donors did not respond to inductive mesoderm. Our results demonstrate that chick flank ectoderm from stage-15 through early stage-20 donors can respond to inductive signals from presumptive wing bud mesoderm to form an apical ridge. This ridge can promote outgrowth of distally complete wings in a substantial proportion of recombinants. This is two stages beyond when the ability to promote outgrowth of distally complete wings appeared to be lost using other methods.
关于鸡胚侧翼外胚层能够对嵴诱导作出反应的阶段，相关报道相互矛盾。使用推定的翅芽或腿芽中胚层作为诱导组织、侧翼外胚层作为反应组织，得到了不同的结果。此外，虽然在一小部分案例中，含有19期侧翼外胚层的重组体产生了不完全的肢体生长，但没有从含有超过18期外胚层的重组体中获得完全的肢体生长。我们重新研究了鸡胚侧翼外胚层何时能够对嵴诱导作出反应并促进完整肢体的生长。为此，我们使用肢体芽前重组技术，将侧翼外胚层与原位鸡胚推定的翅芽中胚层相结合。当从宿主中移除推定的翅芽外胚层且不进行替换时，翅的发育受到抑制。当用第15至18期鸡胚侧翼外胚层替换宿主外胚层时，所有案例中肢体均生长出来；这些重组肢体中有86.4%在远端是完整的。19期侧翼外胚层形成了嵴，并在80.9%的重组体中促进了肢体生长；其中52.9%是远端完整的肢体。通过将早期20期（40体节供体）侧翼外胚层移植到15期宿主中制成的重组体，在60%的案例中产生了肢体生长，其中33.3%在远端是完整的。来自更老供体的移植外胚层对诱导性中胚层没有反应。我们的结果表明，来自第15期至早期20期供体的鸡胚侧翼外胚层能够对推定的翅芽中胚层的诱导信号作出反应，形成顶端嵴。这个嵴能够在相当比例的重组体中促进远端完整翅的生长。这比使用其他方法时促进远端完整翅生长的能力似乎丧失的阶段晚了两个阶段。
